1. Field of the Invention
The invention relates to a pneumatic motor unit having an integrated voltage generator. In particular, the invention concerns a pneumatic motor unit wherein the motor has a pulsating exhaust air outlet flow, for example a vane motor.
2. Description of Related Art
Pneumatic motor units of the above mentioned type are predominant in pneumatic power tools like power wrenches, grinders etc. but are frequently used also in process industry. In many applications there is a demand for obtaining accurate and precise information of the motor operation and/or the actual status of the motor unit. Preferably, this is accomplished by using electrically actuated operation monitoring means for obtaining data of the motor speed, the power shut off etc. and/or means for indicating accumulated operation time, motor temperature etc. Such operation and status monitoring means is dependent on signals from signal emitting sensors on the motor unit. Using sensors of this type is no problem in electrically powered tools where electric power is always accessible, but using sensors and transferring data in pneumatic motor units is not possible unless there is especially provided electric voltage, either via a cable connection with an external electric power source or by providing a voltage generating means integrated in the motor unit itself.
In some applications it is not practical or suitable to use cables, routed separately or in connection with a pressure air conduit, for supplying electric power to the motor unit. This means that in such applications there has to be provided a voltage generating means integrated in the motor unit itself. Certain data related to motor unit operation parameters or to the status of the motor unit may be transferred to a remote system via a wireless communication equipment including a transceiver provided onboard the motor unit and powered by the integrated voltage generating means.
An alternative to supply electric power via a cable would be to provide the motor unit with an onboard battery. However, batteries are rather space demanding, and a battery of small enough dimensions would have a restricted service life and would do neither be able to provide peak currents of magnitudes required for powering sensors and/or wireless communication equipments.
An example on pneumatic motor units with an integrated voltage generating means is described in U.S. Pat. No. 6,840,723. This known motor unit forms a part of a milling tool spindle and comprises a pneumatic turbine, wherein the turbine rotor is provided with a permanent magnet arranged to cooperate with a stationary coil to form a voltage generating means. The magnitude of the voltage generated by this device is speed dependent and is used for activating a speed governing air inlet valve.
This prior art device is disadvantageous in that it requires a specific design of the rotor for attaching the magnet, and that the location of the coil is restricted to a well defined disposition relative to the motor rotor. This means that the design of the motor is very much dependent on the design of the voltage generating device. A further drawback of this known voltage generating device is the instability of the permanent magnet. Such magnets tend to loose power over time and as a result of impacts, which makes the operation and the output voltage less reliable. Magnets also attract and gather ferrous particles which tend to clog up the motor and impair the motor operation.